1. Technical Field
The present disclosure relates to the field of waste treatment, and can be used in the chemical industry for the production of carbon black, but also in the rubber industry for the production of components made of rubber mixtures.
2. Description of the Related Art
Several methods for treating scrap tires have been described in the prior art. In particular, U.S. Pat. No. 5,087,436 presents a vacuum pyrolysis method for obtaining carbon soot with temperatures of between 490 and 510° C., an absolute pressure of 5 kPa, an iodine absorption number of between 0.13 and 0.15 kg/kg, a dibutyl phthalate number (80-100) of between 5 and 10 m3/kg, and a tinting strength of between 55 and 63.
The method described in this patent has several drawbacks, including significant energy expenditure during the process and the complexity of introducing the waste into the reactor because of the need to create and maintain the vacuum in the combustion chamber.
Another method for heat treating scrap tires and a device for implementing it are described in Patent RU 2269415, which obtains solid carbon residues (soot) with the following characteristics: iodine number (ml/100 g)—112, light transmittance of toluene extract (%)—98, dibutyl phthalate absorption (ml/100 g)—93.
This method consists of pyrolysis of scrap tires in a reactor at temperatures between 550 and 800° C. in a reducing gas medium obtained by a reducing gas generator, by combustion of the gases containing hydrocarbons and separation of the pyrolysis products. At least part of the gaseous pyrolysis products exiting the reactor with the liquid hydrocarbon vapors is fed to the reducing gas generator and to the heat unit. At least part of the fumes exiting the heat unit is supplied to the reducing gas generator and the reactor.
The scrap tire heat treatment unit that implements this method comprises a reactor, a system for discharging the gases that form in the reactor, a reducing gas generator connected to the reactor, a crushed tire supply system, and a receiving tray for solid pyrolysis residues. The unit is equipped with a heating device that has means for discharging waste gases, the system for evacuating the gases formed in the reactor being connected to the reducing gas generator and the reactor.
The disadvantages of this method lie in the significant energy expenditures required to implement the method due to the need to produce a reducing gas by incomplete combustion of hydrocarbons, as well as the complexity of introducing the waste into the reactor.
Patent RU 2174911 describes another method for treating waste rubber, including thermal decomposition in a gas-vapor medium, separation of the decomposition products into solid and gaseous products, feeding of solid decomposition products into an activation furnace while simultaneously supplying steam to a furnace in an amount between 0.8 and 1.6 kg per kilogram of solid decomposition products, evacuation of the gas mixture from the activation furnace with a mass ratio for the mixture of between 3 and 0.6 for water vapor and 1 for activation gas, and their use as the gas-vapor medium for the waste decomposition, the feeding into the activation furnace—while simultaneously supplying solid decomposition products and steam—of waste rubber in an amount between 0.05 and 0.20 kg of waste per 1 kg of solid products, leading to the production of activated charcoal.
The disadvantages of this method include high energy consumption when the method is carried out and significant emission of harmful combustion products into the environment.
Patent RU 2139187 describes a heat treatment method for scrap tires in which the tires are loaded into a reactor where the material undergoes pyrolysis at temperatures between 550 and 800° C. in the presence of a reducing gas at a ratio of reducing gas/material of 0.20-0.45:1. The pyrolysis products are then separated and the solid residues are unloaded. Once pyrolysis is completed, steam superheated to temperatures between 250 and 300° C. is added in amounts between 0.03-0.12:1 relative to the loaded material. The reducing gas is produced by incomplete combustion of hydrocarbons a=0.4-0.85.
However, this method has several disadvantages. In fact, it is accompanied by high consumption of energy, especially because of the need to produce reducing gas by incomplete combustion of hydrocarbons. Environmentally harmful gases are emitted at the end of the incomplete combustion of these hydrocarbons. Soot of relatively low quality is produced compared with the large amount of ash (8-14 mass %), and in addition that soot is not eliminated as part of this method. For this reason, additional purification of the soot from the ash is necessary, resulting in additional energy costs.
A method for producing carbon black, hydrocarbon fuel components, and raw materials for the chemical industry from industrial and household waste containing rubber is described in patent RU 2352600. This method consists of thermolysis of crumb rubber fluidized in a vertical stream of solvent, liquefying the mixture containing alkyl aromatic hydrocarbons. The solvent circulates between the crumb rubber and the carbon black. The thermolysis products are separated from the carbon black. The thermolysis is carried out at temperatures between 320 and 420° C., with pressures between 3.8 and 4.2 MPa, and in proportions of the mass of solvent to crumb rubber that are greater than or equal to 1.0. In this method, the solvent is both a liquefying agent and a heat transfer agent, carrying away all thermolysis products in the general stream from the reactor. The carbon black that is produced has a composition close to the composition of the soot used in rubber production.
This method also has disadvantages. High energy consumption is associated with creating the fluidized layer by pumping the heat transfer agent-solvent through the crumb rubber and carbon black, and with regeneration of the heat transfer agent-solvent, involving separation of the latter from the waste thermolysis products. Significant amounts of fumes are emitted into the environment. The relatively low quality of the carbon black produced is similar to the soot used in the production of rubber but cannot be considered a complete substitute, since it contains a large amount of ash in the form of zinc oxide, iron oxide, silicon oxide, etc.
Another method of soot production is described in patent RU 747868. This method consists of pyrolysis of solid hydrocarbon raw materials (waste polymer compositions) at temperatures between 400 and 1500° C., with formation of carbon residues, release of gas-vapor products, and crushing of carbon residues in the stream of gas-vapor products at temperatures between 350 and 400° C., pyrolysis of the waste being carried out by the gas-vapor mixture which is composed of (vol. %):
Superheated steam35-50Carbon dioxide 5-10Carbon monoxide1-3Oxygen0.1-2.0Nitrogenthe remainder
The gas-vapor products from pyrolysis of waste undergo thermal decomposition at temperatures between 1400 and 1500° C.
The disadvantages associated with this method are high energy consumption, resulting in particular from the high temperatures used during pyrolysis (up to 1500° C.). Significant amounts of environmentally harmful gases are emitted due to thermal decomposition of the gas-vapor products. The soot produced is of relatively low quality, due to the large amount of impurities in the form of ash.
Another method is described in patent RU 2276170. This last method includes thermal decomposition of waste in a reactor in a gas-vapor medium, separation of the decomposition products into gas-vapor products and solid carbon residue, and crushing of the carbon residues.
The oil is extracted from the gas-vapor products by condensation and then undergoes thermal decomposition into soot and gas at temperatures of 900-2000° C. After the oil is released, the gas-vapor products are burned together with the carbon residues, and the soot is obtained by filtration of the combustion products.
After separation of the oil, the combustion of the gas-vapor products together with the crushed carbon residues is carried out with an excess air coefficient of between 0.4 and 0.9, yielding the lower quality of soot, or carbon black, that results from the significant carbon dioxide losses associated with high oxygen levels during combustion.
Beforehand, prior to crushing the carbon residues, metal is extracted from the carbon residues by magnetic separation.
The gases from the thermal decomposition of the oil are burned and the combustion products are used as a heat transfer agent for heating the outside of the reactor.
The disadvantages associated with this method again lie in the high energy consumption to produce 1 kg of soot and the large amount of carbon residues burned without soot formation during the common combustion with the gas-vapor products; the complexity in feeding waste into the reactor due to the need to extract oil from the gas-vapor products using special equipment; the significant emission of harmful combustion products into the environment, caused by the large amount of material burned (gases from the thermal decomposition of the oil, the gas-vapor products, a portion of the crushed carbon residues); and the relatively poor quality of the carbon black produced after combustion of a portion of the crushed carbon residues, since the proportion of carbon in the soot that forms is lower and the ash content is higher.